Battery coolant circuit control

ABSTRACT

A vehicle includes a refrigerant system having a chiller and a coolant system having a chiller loop and a radiator loop. The chiller loop is arranged to circulate coolant through the chiller, and the radiator loop is arranged to circulate coolant through a battery, a radiator, and a bypass valve connected to a bypass conduit. A controller is configured to, in response to an ambient-air temperature exceeding a battery-coolant temperature, actuate the valve to circulate coolant to the bypass conduit to skip the radiator.

TECHNICAL FIELD

The present disclosure relates to a control strategy and method foroperating at least one valve of a battery-coolant system to controlcoolant flow to one or both of a radiator, and a battery chillerassociated with an air-conditioning system of a vehicle.

BACKGROUND

The need to reduce fuel consumption and emissions in automobiles andother vehicles is well known. Vehicles are being developed that reducereliance or completely eliminate reliance on internal-combustionengines. Electric and hybrid vehicles are one type of vehicle currentlybeing developed for this purpose. Electric and hybrid vehicles include atraction motor that is powered by a traction battery. Traction batteriesrequire a thermal-management system to thermally regulate thetemperature of the battery cells.

SUMMARY

According to one embodiment, a vehicle includes a refrigerant systemhaving a chiller and a coolant system having a chiller loop and aradiator loop. The chiller loop is arranged to circulate coolant throughthe chiller, and the radiator loop is arranged to circulate coolantthrough a battery, a radiator, and a bypass valve connected to a bypassconduit. A controller is configured to, in response to an ambient-airtemperature exceeding a battery-coolant temperature, actuate the valveto circulate coolant to the bypass conduit to skip the radiator.

According to another embodiment, a thermal-management system for atraction battery of a hybrid vehicle includes a refrigerant subsystemand a coolant subsystem. The refrigerant subsystem includes acompressor, a condenser, a battery chiller, and an evaporator. Thecoolant subsystem includes a proportioning valve having first and secondoutlets, and an inlet connected in fluid communication with an outletside of the traction battery via an outlet conduit. A temperature sensoris disposed on the outlet conduit and is configured to output a signalindicative of a coolant temperature. The coolant subsystem furtherincludes a chiller loop and a radiator loop. The chiller loop isconnected in fluid communication with the first outlet and is arrangedto convey coolant through the chiller to transfer heat from the coolantsubsystem to the refrigerant subsystem. The radiator loop is connectedin fluid communication with the second outlet and is arranged to conveycoolant through the radiator to transfer heat from the coolant subsystemto outside air. The radiator loop has a bypass valve configured to routecoolant around the radiator via a bypass line when the valve is actuatedto a bypass position and configured to route coolant to the radiatorwhen the valve is actuated to a radiator position. A controller isconfigured to, in response to the proportioning valve directing at leasta portion of the coolant to the second outlet and the outside airtemperature exceeding the coolant temperature, actuate the bypass valveto the bypass position.

According to yet another embodiment, a method of controlling athermal-management system includes circulating refrigerant through achiller. The method further includes circulating coolant through atraction battery, a radiator, the chiller, a proportioning valve, and abypass valve. The method also includes, in response to the proportioningvalve routing at least a portion of the coolant to the bypass valve andan ambient-air temperature exceeding a temperature of the coolant,actuating the bypass valve to a bypass position where the coolantbypasses the radiator.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of an example hybrid vehicle.

FIG. 2 is a schematic diagram of a battery thermal-management system anda climate-control system of a vehicle.

FIG. 3 is a table of climate load.

FIG. 4 is a table of chiller-capacity.

FIG. 5 is a flow chart for controlling the battery thermal-managementsystem.

FIG. 6 is a flow chart for translating chiller capacity to a valveposition of the proportioning valve.

DETAILED DESCRIPTION

Embodiments of the present disclosure are described herein. It is to beunderstood, however, that the disclosed embodiments are merely examplesand other embodiments can take various and alternative forms. Thefigures are not necessarily to scale; some features could be exaggeratedor minimized to show details of particular components. Therefore,specific structural and functional details disclosed herein are not tobe interpreted as limiting, but merely as a representative basis forteaching one skilled in the art to variously employ the presentinvention. As those of ordinary skill in the art will understand,various features illustrated and described with reference to any one ofthe figures can be combined with features illustrated in one or moreother figures to produce embodiments that are not explicitly illustratedor described. The combinations of features illustrated providerepresentative embodiments for typical applications. Variouscombinations and modifications of the features consistent with theteachings of this disclosure, however, could be desired for particularapplications or implementations.

FIG. 1 depicts a schematic of a typical plug-in hybrid-electric vehicle(PHEV). Certain embodiments, however, may also be implemented within thecontext of non-plug-in hybrids and fully-electric vehicles. The vehicle12 includes one or more electric machines 14 mechanically connected to ahybrid transmission 16. The electric machines 14 may be capable ofoperating as a motor or a generator. In addition, the hybridtransmission 16 may be mechanically connected to an engine 18. Thehybrid transmission 16 may also be mechanically connected to a driveshaft 20 that is mechanically connected to the wheels 22. The electricmachines 14 can provide propulsion and deceleration capability when theengine 18 is turned on or off. The electric machines 14 also act asgenerators and can provide fuel economy benefits by recovering energythrough regenerative braking. The electric machines 14 reduce pollutantemissions and increase fuel economy by reducing the work load of theengine 18.

A traction battery or battery pack 24 stores energy that can be used bythe electric machines 14. The traction battery 24 typically provides ahigh-voltage direct current (DC) output from one or more battery cellarrays, sometimes referred to as battery cell stacks, within thetraction battery 24. The battery cell arrays may include one or morebattery cells.

The battery cells, such as a prismatic, pouch, cylindrical, or any othertype of cell, convert stored chemical energy to electrical energy. Thecells may include a housing, a positive electrode (cathode) and anegative electrode (anode). An electrolyte may allow ions to movebetween the anode and cathode during discharge, and then return duringrecharge. Terminals may allow current to flow out of the cell for use bythe vehicle.

Different battery pack configurations may be available to addressindividual vehicle variables including packaging constraints and powerrequirements. The battery cells may be thermally regulated with athermal-management system. Examples of thermal-management systemsinclude air cooling systems, liquid cooling systems and a combination ofair and liquid systems.

The traction battery 24 may be electrically connected to one or morepower electronics modules 26 through one or more contactors (not shown).The one or more contactors isolate the traction battery 24 from othercomponents when opened and connect the traction battery 24 to othercomponents when closed. The power-electronics module 26 may beelectrically connected to the electric machines 14 and may provide theability to bi-directionally transfer electrical energy between thetraction battery 24 and the electric machines 14. For example, a typicaltraction battery 24 may provide a DC voltage while the electric machines14 may require a three-phase alternating current (AC) voltage tofunction. The power-electronics module 26 may convert the DC voltage toa three-phase AC voltage as required by the electric machines 14. In aregenerative mode, the power electronics module 26 may convert thethree-phase AC voltage from the electric machines 14 acting asgenerators to the DC voltage required by the traction battery 24. Thedescription herein is equally applicable to a fully-electric vehicle. Ina fully-electric vehicle, the hybrid transmission 16 may be a gear boxconnected to an electric machine 14 and the engine 18 is not present.

In addition to providing energy for propulsion, the traction battery 24may provide energy for other vehicle electrical systems. A typicalsystem may include a DC/DC converter module 28 that converts the highvoltage DC output of the traction battery 24 to a low voltage DC supplythat is compatible with other vehicle components. Other high-voltageloads, such as compressors and electric heaters, may be connecteddirectly to the high-voltage supply without the use of a DC/DC convertermodule 28. In a typical vehicle, the low-voltage systems areelectrically connected to an auxiliary battery 30 (e.g., a 12 voltbattery).

A battery energy control module (BECM) 33 may be in communication withthe traction battery 24. The BECM 33 may act as a controller for thetraction battery 24 and may also include an electronic monitoring systemthat manages temperature and charge state of each of the battery cells.The traction battery 24 may have a temperature sensor 31 such as athermistor or other temperature sensor. The temperature sensor 31 may bein communication with the BECM 33 to provide temperature data regardingthe traction battery 24.

The vehicle 12 may be recharged by a charging station connected to anexternal power source 36. The external power source 36 may beelectrically connected to electric vehicle supply equipment (EVSE) 38.The external power source 36 may provide DC or AC electric power to theEVSE 38. The EVSE 38 may have a charge connector 40 for plugging into acharge port 34 of the vehicle 12. The charge port 34 may be any type ofport configured to transfer power from the EVSE 38 to the vehicle 12.The charge port 34 may be electrically connected to a charger oron-board power conversion module 32. The power conversion module 32 maycondition the power supplied from the EVSE 38 to provide the propervoltage and current levels to the traction battery 24. The powerconversion module 32 may interface with the EVSE 38 to coordinate thedelivery of power to the vehicle 12. The EVSE connector 40 may have pinsthat mate with corresponding recesses of the charge port 34.

The various components discussed may have one or more controllers tocontrol and monitor the operation of the components. The controllers maycommunicate via a serial bus (e.g., Controller Area Network (CAN)) orvia dedicated electrical conduits. The controller generally includes anynumber of microprocessors, ASICs, ICs, memory (e.g., FLASH, ROM, RAM,EPROM and/or EEPROM) and software code to co-act with one another toperform a series of operations. The controller also includespredetermined data, or “look up tables” that are based on calculationsand test data, and are stored within the memory. The controller maycommunicate with other vehicle systems and controllers over one or morewired or wireless vehicle connections using common bus protocols (e.g.,CAN and LIN). Used herein, a reference to “a controller” refers to oneor more controllers.

The traction battery 24 and other vehicle component are thermallyregulated with one or more thermal-management systems. Examplethermal-management systems are shown in the figures and described below.Referring to FIG. 2, a vehicle 12 includes a thermal-management system56. The thermal-management system 56 can be employed to manage thermalloads generated by various vehicle components, such as the batteryassembly 24, powertrain components, and power-electronic components. Forexample, the thermal-management system 56 can selectively circulatecoolant to the battery assembly 24 to either cool or heat the batteryassembly depending on operating conditions.

The thermal-management system 56 may include one or more vehiclecontrollers 78. While schematically shown as a single module in theillustrated embodiment, the controller 78 may be part of a largercontrol system and may be controlled by various other controllersthroughout the vehicle, such as a vehicle-system controller (VSC) thatincludes a powertrain-control unit, a transmission control unit, anengine control unit, a BECM, etc. It should be understood that thecontroller 78 and one or more other controllers can collectively bereferred to as “a controller” that controls, such as through a pluralityof integrated algorithms, various actuators in response to signals fromvarious sensors to control functions associated with the vehicle, and inthis case, with a thermal-management system 56. The various controllersthat make up the VSC can communicate with one another using a common busprotocol (e.g., CAN).

In one embodiment, the battery thermal-management system 56 includes acoolant subsystem 58 and a refrigerant subsystem 60. These two loops mayoperate in tandem or independently of each other depending upon thebattery cooling requirements, the ambient-air temperature, and otherfactors. The refrigerant subsystem 60 may be a vapor-compression heatpump that circulates a refrigerant transferring thermal energy tovarious components of the climate-control system. The refrigerantsubsystem 60 may be the air-conditioning (AC) system for the cabin.Utilizing the cabin AC may be more cost effective than having adedicated refrigerant system for the traction battery 24. The coolantsubsystem 58, or coolant loop, circulates coolant to the batteryassembly 24. The coolant may be a conventional type of coolant mixture,such as water mixed with ethylene glycol. Other coolants could also beused by the coolant subsystem 58. The coolant subsystem 58 may include aradiator 64, a proportioning valve 66, a bypass valve 100, a pump 68, aninlet coolant temperature sensor 70, the battery 24, an outlet coolanttemperature sensor 99 and a chiller 76. The coolant subsystem 58 mayalso include additional components.

In operation, warm coolant exits an outlet 63 of the battery 24. Thewarm coolant is circulated to the radiator 64 via line 72 when the valve66 is in a first set of positions and the valve 100 is in a radiatorposition. The warm coolant is cooled within the radiator 64 by airflowtraveling across the fins to effectuate heat transfer between theairflow and the warm coolant. Cool coolant exits the radiator 64 andenters line 67 for recirculation to the pump 68. The radiator 64 and atleast a portion of lines 67, 72, 79, and 110 may be referred to as theradiator loop 101.

The sensor 70 may be positioned near an inlet 61 of the battery pack 24.The sensor 70 is configured to monitor the temperature of the coolantthat is returned to the battery pack 24. In some embodiments, multiplesensors may be used to measure coolant temperature at various locations.The battery pack 24 may also include one more sensors 65. The sensors 65monitor the temperatures of various battery cells (not shown) of thebattery pack 24.

The radiator loop 101 may include a radiator-bypass loop 103 that allowscoolant to skip the radiator. Unlike an engine, which operates attemperatures well above ambient, traction batteries operate attemperature in the range of 15 to 30 degrees Celsius. As such, theambient-air temperature may exceed the battery-coolant temperature (BCT)with regularity depending upon the season and geographic location. Whenthe ambient-air temperature exceeds the BCT, the radiator adds heat tothe coolant. The bypass loop 103 allows the radiator to be skipped whenthe air temperature exceeds the BCT to prevent the radiator 64 fromadding heat to the subsystem 58. The bypass loop 103 also allows theradiator 64 to be skipped when the battery temperature is below athreshold value.

The bypass loop 103 includes a two-way valve (bypass valve) 100including an inlet 108 connected to conduit 79, a first outlet 104connected to conduit 110, and a second outlet 106 connected to thebypass conduit 102. The bypass valve 100 is operable to route coolantbetween the first and second outlets depending upon a position of thevalve. The valve 100 includes an electronically controllable actuatorsuch as a solenoid or electric motor. The controller 78 may includeprogramming to operate the valve 100. For convention, the valve mayinclude a radiator position where the valve routes coolant to the outlet104, and a bypass position (or skip position) where the valve routescoolant to outlet 106. The valve 100 may be a two position valve thatroutes 100% of the coolant to either outlet 104 or outlet 106 dependingupon valve position. The bypass conduit 102 connects between conduit 79and conduit 67 to route coolant around the radiator when the valvedirects coolant to outlet 106.

The coolant subsystem 58 further includes a chiller loop 74 including aline 75 connected between line 72 and line 67. The line 75 allowscoolant to bypass the radiator 64 and conduit 102, and instead,circulate through the chiller 76. The valve 66 controls the circulationof coolant through the chiller 76. The valve 66 may be a solenoid valvethat is electrically controlled by the controller 78. The valve 66 mayinclude a stepper motor for increasing or decreasing the opening of thevalve. Other types of valves could alternatively be utilized within thecoolant subsystem 58. The valve 66 includes an inlet 71 connected toline 72, a first outlet 73 connected to line 79, and a second outlet 77connected to line 75. The valve 66 is configured such that each of theoutlets 73, 77 selectively receive a proportion, between 0 and 100percent inclusive, of the coolant flowing through the valve 66 dependingupon a position of the valve. By adjusting the proportion of coolantdivided between the outlets, the amount of coolant flowing through thechiller 76 and line 79 can be controller according to algorithms storedin memory of the controller 78.

The chiller 76 exchanges heat with the refrigerant subsystem 60 toprovide a chilled coolant during certain conditions. For example, whenthe battery temperature exceeds a predefined threshold and the cabin ACsystem 60 has capacity, the valve 66 may be actuated to circulate atleast some coolant to the chiller 76. A portion of the warm coolant fromthe battery pack 24 may enter the chiller line 75 and exchange heat witha refrigerant of the refrigerant subsystem 60 within the chiller 76 todissipate heat.

The battery chiller 76 may have any suitable configuration. For example,the chiller 76 may have a plate-fin, tube-fin, or tube-and-shellconfiguration that facilitates the transfer of thermal energy withoutmixing the heat-transfer fluids in the coolant subsystem 58 and therefrigerant subsystem 60.

The refrigerant subsystem 60, may include a compressor 80, a condenser82, at least one cabin evaporator 84, the chiller 76, a first expansiondevice 86, a shutoff valve 87, a second expansion device 88, and asecond shutoff valve 91. The compressor 80 pressurizes and circulatesthe refrigerant through the refrigerant subsystem 60. The compressor 80may be powered by an electrical or non-electrical power source. Apressure sensor 95 may monitor the pressure of the refrigerant exitingthe compressor 80.

The refrigerant exiting the compressor 80 may be circulated to thecondenser 82 by one or more conduits. The condenser 82 transfers heat tothe surrounding environment by condensing the refrigerant from a vaporto a liquid. A fan 85 may be selectively actuated to circulate airflowacross the condenser 82 to further effectuate heat transfer between therefrigerant and the airflow. The fan 85 may be arranged to circulate airover the radiator 64 as well.

At least a portion of the liquid refrigerant that exits the condenser 82may be circulated through the first expansion device 86 (depending uponthe position of valve 87) and then to the evaporator 84. The firstexpansion device 86 is adapted to change the pressure of therefrigerant. In one embodiment, the first expansion device 86 is anelectronically controlled expansion valve (EXV). In another embodiment,the first expansion device 86 is a thermal expansion valve (TXV). If theexpansion device is an EXV, the shutoff valve can be omitted. The liquidrefrigerant is vaporized from liquid to gas, while absorbing heat,within the evaporator 84. The gaseous refrigerant may then return to thecompressor 80. The refrigerant subsystem may include an evaporatortemperature sensor 89 that is electrically connected to the controller78. The sensor 89 outputs a signal indicative of the evaporatortemperature. The controller 78 may operate the system based on signalsreceived from sensor 89. Alternatively, the valve 87 may be closed tobypass the evaporator 84.

Another portion of the liquid refrigerant exiting the condenser 82 (orall of the refrigerant if the valve 87 is closed) may circulate throughthe second expansion device 88 and enter the chiller 76 if the valve 91is open. The second expansion device 88, which may also be an EXV orTXV, is adapted to change the pressure of the refrigerant. Therefrigerant exchanges heat with the coolant within the chiller 76 toprovide the chilled coolant to the battery 24 during a chiller mode.

The battery-cooling system 58 may be programmed to preferably cool thebattery 24 via only the radiator 64 whenever possible, because coolingthe battery with the radiator 64 may consume less energy than with thechiller 76, which may increase the range of the vehicle. There are manysituations, however, where radiator cooling alone is insufficient tocool the battery 24. These situations include when the batterytemperature or ambient-air temperature exceeds the predefinedtemperature thresholds of the battery and the ambient air, respectively,and when the load (discharge or recharge) on the battery causes thebattery to generate more heat than can be dissipated with the radiatoralone. Thus, in many situations, the chiller 76 must provide at leastsome of the cooling for the battery 24. The proportioning valve 66 iscapable of routing ratios of coolant between the radiator and thechiller to effectuate cooling of the battery 24 in the most efficientmanner while preventing relatively large discharge air temperatureswings in the cabin. The proportioning valve 66 may be controlled by analgorithm that minimizes the step change of the air blown into the cabinby prioritizing cabin cooling and throttling coolant flow to the chillerbased on AC capacity availability.

In systems in which the battery chiller is in fluid communication withthe cabin AC system, as is the case in the illustrated embodiment, apotential for negatively affecting the temperature of the cabin air ispossible if the AC system does not have enough capacity to cool both thecabin and the battery at their respective loads. For example, on a hotday, simultaneously cooling the battery and the passenger cabin via theAC system may cause the outlet temperature of the cabin evaporator 84 toincrease beyond a target temperature, which causes the air blowing intothe cabin to be warmer than that requested by the occupants. Theoccupants may find it dissatisfying when the cabin temperature is notconforming with the demand temperature. As such, carmakers must choosebetween satisfying cabin demands versus satisfying battery demands insituations in which the combined load exceeds the capacity of therefrigerant system.

In one embodiment, the system is designed to prioritize the cabin demandover the battery demand. Here, the controller 78 is configured todetermine a total capacity of the AC system, the amount of the totalcapacity being used by the cabin evaporator (which may be calledevaporator capacity), and a chiller capacity that is available to thechiller if needed. The chiller capacity is the reserve capacity of therefrigerant system to accept additional heat from the chiller. Thechiller capacity is equal to the total system capacity minus theevaporator capacity. The controller 78 may be programmed to determinethe chiller capacity as a function of the cabin thermal load, and atemperature differential between a target evaporator temperature and ameasured evaporator temperature. The target temperature of evaporator 84is based on the cabin temperature requested by the driver, ambient-airtemperature, sun load, and climate-control mode. For example, if thedriver requests a 21 degrees Celsius cabin temperature, the controllerincludes mapping indicating a target evaporator temperature of 2-9degrees Celsius range with 6 degrees being a typical target evaporatorvalue. The cabin thermal load is a function of the temperature of theambient air and the speed of the cabin blower that circulates air overthe evaporator 84. An example high load occurs when the blower is onHIGH and the ambient air is above 30 degrees Celsius, and an example lowload occurs when the blower is on LOW and the ambient air is below 20degrees Celsius. The thermal load could also take into account ambientair temperature, sun load, cabin temperature setpoint, sun load, and thenumber of vehicle occupants.

The controller is further configured to route an appropriate amount ofcoolant through the chiller 76 in order to not exceed the chillercapacity. The valve 66 is used to control the percentage of coolantflowing to the chiller versus the percentage of coolant bypassing thechiller via the radiator loop. The capacity transferred through thechiller is directly proportional to the mass flow rate of coolantcirculating through the chiller and the temperature of the coolant.Depending upon the condition of the cabin AC system 60, theproportioning valve 66 may send anywhere between zero and 100 percent ofthe coolant to the chiller based on battery demand and cabin demand. Ifno chiller capacity is available, the valve 66 routes 100% of thecoolant to line 79, and the battery-coolant system may attempt to coolthe battery using the radiator 64 in conjunction with the fan 85 ifpossible. In some instances, the radiator and fan may be unable toachieve a sufficiently low coolant temperature for a given battery loador radiator cooling may be unavailable. To prevent overheating, thecontroller 78 may power limit the battery to prevent overheating.

Referring to FIG. 3, an example load table 116 is shown. The load table116 may be stored in memory of the controller 78. The controller 78 mayinclude one or more load tables that are selectively used duringdifferent operating conditions. In the table 116, the load increaseswith increasing air temperatures and with increasing blower speeds. Theblower speed may be represented as a percentage.

Referring to FIG. 4, an example chiller-capacity table 118 is shown. Thetable 118 may be stored in memory of the controller 78. The controller78 may include one or more tables that are selectively used duringdifferent operating conditions. The Y-axis is the load, which isdetermined using table 116 for example, and the X-axis is thetemperature differential between the measured temperature of theevaporator 84 and the target temperature of the evaporator 84. Ratherthan expressing the capacity as a numerical value of capacity, table 118categorizes the calculated chiller capacity into a plurality ofpredefined ranges and assigns each of the ranges a number. For example,the chiller capacity can be grouped into four ranges labeled zero, one,two, and three. The zeros correspond to no chiller capacity and thethrees correspond to full chiller capacity. The ones and twos correspondto intermediate chiller capacities. Having four ranges is merely anon-limiting example; the system may include more ranges to increase theprecision of control. The calibration tables can be interpolated inbetween points. For example, chiller capacity is 0.5 when the evaporatorerror is 1.5 and the load is 45. In some embodiments, algorithmsexecuted by the controller 78 map the chiller capacity from table 118with a valve position of the proportioning valve 66 that is calibratedto provide the desired amount of heat transfer (i.e., capacity) acrossthe chiller 76. In other embodiments, the chiller capacity is used as aclip (or maximum opening). These embodiments will be explained in detailbelow.

FIG. 5 illustrates a flow chart 120 of an algorithm for operating theproportioning valve 66 to achieve a desired chiller capacity. Atoperation 122 the controller calculates an evaporator error. Theevaporator error is the temperature difference between the measuredtemperature (e.g., by sensor 89) of the evaporator 84 and a targettemperature of the evaporator. At operation 124 the cabin load iscalculated using table 116 for example. As described above, the cabinload is a function of the blower speed and the ambient-air temperature.At operation 126 the controller calculates the chiller capacity usingtable 118 for example. The chiller capacity is a function of the loadand the evaporator error. At operation 128 the controller determines ifthe chiller capacity is greater than zero. If the chiller capacity iszero, the chiller cannot be used to cool the battery. As such, controlloops back to the start. If the chiller capacity is greater than zero,control passes to operation 130 and the controller translates thechiller capacity into a position of the proportioning valve.

Translating chiller capacity to a position of the proportioning valve 66can be done in several different ways. In a first embodiment, at leastone of the predefined ranges (i.e., 1 and 2) may include a correspondingpredefined position of the proportioning valve 66. For example, chillercapacities categorized as “one” correspond to a proportioning valveposition that routes 25% of the coolant to the chiller and 75% of thecoolant to the radiator. Chiller capacities categorized as “two”correspond to a proportioning valve position that routes 50% of thecoolant to the chiller and 50% of the coolant to the radiator. Thesevalve-position values are merely examples and are not limiting. Whenchiller capacity is three, the chiller capacity is more than enough tocool the battery and routing too much coolant through the chiller mayovercool the battery. Thus, range 3 may not have a predefined valveposition associated with it. Instead, when the capacity is three, theproportioning valve position may be controlled based on a differencebetween a target battery temperature and a measured battery temperature.

In another embodiment, the proportioning valve position can becontrolled using proportion integral (PI) control. Referring to FIG. 6,a module of the controller 78 receives a measured battery-coolanttemperature 144 (e.g., signal from sensor 70 or 99) and a target batterycoolant temperature 146. The target temperature 146 is set by thebattery based on battery temperature, battery load, and ambient-airtemperature. The measured temperature 144 is subtracted from the targettemperature 142, or vice versa, to determine a temperature error 148.The error 148 is fed into a PI controller 150, which outputs apreliminary valve position (PVP) 152 of the proportioning valve 66 thatis calculated to provide the desired battery temperature. The PVP 152 isdetermined without regard to the chiller capacity. As such, blindlyactuating the valve to the PVP may negatively affect cabin-airtemperature. To prevent this, the PVP is compared to, and if necessaryclipped by, a maximum valve position of the proportioning valve. Themaximum valve position is based on the chiller capacity as calculated bytable 118 for example. At least one of the chiller-capacity ranges mayhave a corresponding maximum valve position which is calculated atoperation 130. For example, the maximum valve position for range one is25% of coolant to the chiller, and for range two is 50% of coolant tothe chiller. Range 3 may not have an associated maximum valve positionbecause the chiller capacity exceeds a maximum battery thermal load. Orrange 3 may have a maximum valve position of 100%. At 154, thecontroller determines if the PVP is greater than the maximum valveposition. If yes, the PVP is clipped and the proportioning valve is setto the maximum valve position at 156. If no, the proportioning valve isset to the PVP at 158.

Referring back to FIG. 5, at operation 132, the proportioning valve 66is actuated to the position determined at step 152 or step 154. Theproportioning valve 66 may be actuated by a stepper motor associatedtherewith or a similar mechanism.

At operation 134, the controller determines if the chiller capacity isthree. When chiller capacity is three, the radiator 64 is not requiredto cool the coolant and the bypass valve may be actuated to the bypassposition. In some embodiments, coolant may be circulated through theradiator when the chiller capacity is three. If no at operation 134,control passes to operation 138 and the controller determines if thecoolant exiting the battery (BCT_(out)) exceeds the temperature of theambient-air. If no, control passes to operation 140 and the bypass valve100 is actuated to the bypass position to prevent the radiator fromheating coolant. At operation 142 the fan is de-energized (if it is ON)as the radiator is not functioning. Despite the determination atoperation 142, the fan may be energized by another control system ifanother heat exchanger (e.g., the condenser) requires the fan to berunning. If yes at operation 138, the controller actuates the bypassvalve to a radiator position at operation 144. If the controllerdetermines that the radiator requires the assistance of the fan, the fanis energized at operation 146. The fan speed may be based on BCT_(out)and the ambient-air temperature.

While example embodiments are described above, it is not intended thatthese embodiments describe all possible forms encompassed by the claims.The words used in the specification are words of description rather thanlimitation, and it is understood that various changes can be madewithout departing from the spirit and scope of the disclosure. Aspreviously described, the features of various embodiments can becombined to form further embodiments of the invention that may not beexplicitly described or illustrated. While various embodiments couldhave been described as providing advantages or being preferred overother embodiments or prior art implementations with respect to one ormore desired characteristics, those of ordinary skill in the artrecognize that one or more features or characteristics can becompromised to achieve desired overall system attributes, which dependon the specific application and implementation. These attributes caninclude, but are not limited to cost, strength, durability, life cyclecost, marketability, appearance, packaging, size, serviceability,weight, manufacturability, ease of assembly, etc. As such, embodimentsdescribed as less desirable than other embodiments or prior artimplementations with respect to one or more characteristics are notoutside the scope of the disclosure and can be desirable for particularapplications.

What is claimed is:
 1. A thermal-management system for a tractionbattery of a hybrid vehicle, the thermal-management system comprising: arefrigerant subsystem including a compressor, a condenser, a batterychiller, and an evaporator; a coolant subsystem including aproportioning valve having first and second outlets, and an inletconnected in fluid communication with an outlet side of the tractionbattery via an outlet conduit, a temperature sensor disposed on theoutlet conduit and configured to output a signal indicative of a coolanttemperature, a chiller loop connected in fluid communication with thefirst outlet and arranged to convey coolant through the chiller totransfer heat from the coolant subsystem to the refrigerant subsystem,and a radiator loop connected in fluid communication with the secondoutlet and arranged to convey coolant through the radiator to transferheat from the coolant subsystem to outside air, the radiator loop havinga bypass valve configured to route coolant around the radiator via abypass line when the valve is actuated to a bypass position andconfigured to route coolant to the radiator when the valve is actuatedto a radiator position; and a controller configured to, in response tothe proportioning valve directing at least a portion of the coolant tothe second outlet and the outside air temperature exceeding the coolanttemperature, actuate the bypass valve to the bypass position.
 2. Thethermal-management system of claim 1, wherein the controller is furtherconfigured to, in response to the outside air temperature being lessthan the coolant temperature, actuate the bypass valve to the radiatorposition.
 3. The thermal-management system of claim 2 further comprisinga fan arranged to circulate the outside air through the radiator,wherein the controller is further configured to activate the fan basedon the coolant temperature and the outside air temperature.
 4. Thethermal-management system of claim 1, wherein the controller is furtherconfigured to, in response to a temperature of the traction batterybeing less than a threshold value, actuate the bypass valve to thebypass position.
 5. The thermal-management system of claim 1 furthercomprising a fan arranged to circulate the outside air through theradiator, wherein the controller is further programmed to de-energizethe fan in response to the bypass valve being in the bypass position. 6.The thermal-management system of claim 1, wherein the controller isfurther configured to actuate the proportioning valve such that thecoolant is proportioned between the first and second outlets based on achiller capacity.
 7. The thermal-management system of claim 6, whereinthe controller is further configured to actuate the proportioning valvesuch the proportion of the coolant circulated to the first outletincreases as the chiller capacity increases.
 8. The thermal-managementsystem of claim 7, wherein the controller is further configured toactuate the proportioning valve such that the proportion of the coolantcirculated to the second outlet increases as the chiller capacitydecreases.
 9. A vehicle comprising: a refrigerant system including achiller; a coolant system including a chiller loop arranged to circulatecoolant through the chiller, and a radiator loop arranged to circulatecoolant through a battery, a radiator, and a bypass valve connected to abypass conduit; and a controller configured to, in response to anambient-air temperature exceeding a battery-coolant temperature, actuatethe valve to circulate coolant to the bypass conduit to skip theradiator.
 10. The vehicle of claim 9, wherein the controller is furtherconfigured to, in response to the ambient-air temperature being lessthan the battery-coolant temperature, actuate the valve to circulatecoolant to the radiator loop and not the bypass conduit.
 11. The vehicleof claim 9, wherein the controller is further configured to, in responseto a temperature of the battery being less than a threshold value,actuate the valve to circulate coolant to the bypass conduit and not theradiator loop.
 12. The vehicle of claim 9, wherein the coolant systemfurther includes a proportioning valve configured to selectively routecoolant to at least one of the chiller loop and the radiator loop. 13.The vehicle of claim 12, wherein the controller is further configured toactuate the proportioning valve such that coolant is proportionedbetween the radiator loop and chiller loop based on a chiller capacity.14. The vehicle of claim 13, wherein the chiller capacity is based on atemperature difference between a measured temperature of a cabinevaporator and a target temperature of the cabin evaporator.
 15. Thevehicle of claim 9, wherein the controller is further configured to, inresponse to a temperature of the battery being less than a thresholdvalue and less than the ambient-air temperature, actuate the valve tocirculate coolant to the bypass conduit and not the radiator loop. 16.The vehicle of claim 9 further comprising a fan arranged to circulateair through the radiator, wherein the controller is further programmedto de-energize the fan in response to the coolant being circulated tothe bypass conduit.
 17. A method of controlling a thermal-managementsystem, comprising: circulating refrigerant through a chiller;circulating coolant through a traction battery, a radiator, the chiller,a proportioning valve, and a bypass valve; and in response to theproportioning valve routing at least a portion of the coolant to thebypass valve and an ambient-air temperature exceeding a temperature ofthe coolant, actuating the bypass valve to a bypass position where thecoolant bypasses the radiator.
 18. The method of claim 17 furthercomprising, in response to the ambient-air temperature being less thanthe temperature of the coolant, actuating the bypass valve to a radiatorposition where the coolant circulates to the radiator.
 19. The method ofclaim 17 further comprising, in response to the bypass valve being inthe bypass position, de-energizing a radiator fan.
 20. The method ofclaim 17 further comprising actuating the proportioning valve such thatthe coolant is proportioned between the radiator and the chiller basedon a chiller capacity.